The present invention relates to a new and improved method for the crown grinding of gear teeth having lengthwise curved teeth, by means of truncated conical-shaped grinding elements or bodies which are individually driven and rotatable about their axes. The grinding elements are mounted in a grinding head rotatable about an axis of rotation and, during grinding, form an outer as well as an inner envelope surface which is coaxially dispositioned with respect to the axis of rotation of the grinding head. The invention further pertains to an improved grinding head for performance of the aforesaid method.
Lengthwise curved teeth of gears are crown ground, in order to exactly define to the extent possible the region of the teeth flanks where there occurs contact with the teeth of a mating gear, the so-called load bearing. In this way, there can be avoided, for instance, one sided load-bearing or load-bearing limited only to the ends of the gear teeth.
Swiss Pat. No. 543,921, discloses a method for grinding and crown grinding of gears, and also an apparatus for the performance of a method of the type generally discussed hereinabove. The grinding of the inner and outer flanks of the gear teeth is accomplished, with this method, simultaneously during one working operation. A grinding head, used for this purpose, contains two groups of truncated cone-shaped grinding elements or bodies. Each group is arranged upon a circle which is concentrically dispositioned with respect to the axis of rotation of the grinding head. In order to perform the grinding operation, a tooth is moved in each instance between a pair of mutually operatively correlated grinding elements or bodies, each such grinding elements or bodies being correlated to a respective one of both groups. With this technique, the grinding elements or bodies rotate about their own axes as well as about the axis of the grinding head.
For crown grinding, the grinding elements are mounted to be movable to-and-fro in the direction of their axes upon the grinding head. This to-and-fro movement is controlled in that the ends of the grinding elements, facing away from the gear to be ground, are guided along ring-shaped control cams or discs, which during rotation of the grinding head, initiates such to-and-fro movements. In other words, the tooth flanks are ground at their ends closer to the tooth root or base of the tooth gap, and the truncated cone-shaped grinding elements grind more intensely also perpendicular to the tooth flanks.
With this technique and this grinding head, the grinding accuracy is impaired by the following explained drawbacks.
Since the ends of the grinding elements or bodies slide upon the control cam or disc transversely with respect to their own axis, during the rotation of the grinding head, the grinding elements and, in particular, their cylindrical shafts or stems, are placed into oscillation. This is so because the mounting of the individual grinding elements cannot be accomplished in a stable manner, as such would be desirable, since very little space is available between the individual grinding elements or bodies in order to provide an effective mounting or support arrangement.
After the dressing of the grinding elements, the spacing between the grinding elements of a pair, as well as the spacing of the individual grinding elements from the axis of rotation of the grinding head, again must be newly adjusted. Since a grinding head contains a large number of pairs of such grinding elements, there must be carried out a corresponding number of adjustments, increasing the probability of faulty settings.
Furthermore, there is known to the art from U.S. Pat. No. 3,440,927 a machine for cutting gears. With this equipment, the inner and outer flanks of the gear teeth are cut with cutters or cutting blades arranged at different radii upon a cutter head. Here, the inner and outer flanks are cut in separate working operations, and the axis of rotation of the cutter head is set in spaced relationship from the related teeth flanks, such spacing corresponding to the radius of the cutter at the cutter head.
This cutting technique is, however, not comparable to the inventive cutting method for crown cutting of gear teeth since the prior art cutting method is applicable to cone gears, and, specifically, serves for tapering the teeth for the teeth gap or spaces in their lengthwise direction.
Other prior art techniques and equipment for cutting gears are demonstrated in U.S. Pat. No. 3,503,301 and German patent publication No. 1,752,775.